Loud-speaker diaphragm support member



May 102 1949 H. s. KNowLEs 2,469,773

LOUD-SPEAKER DIAPHRAGM SUPPORT MEMBER Original Filed June 4. 1934 si /42 i Patented May 10, 1949 LOUDSPEAKER DIAPHRAGM SUPPORT MEMBER Hugh S. Knowles, River Forest, Ill., assigner to Jensen Manufacturing Company, a corporation of Nevada Original application June 4, 1934, Serial N0.

Divided and this application August 12, 1942, Serial No. 454,527

7 Claims.

This invention relates to a loud speaker and is a division of my application Serial No. 728,993, filed June 4, 1934, now Patent No. 2,295,483, dated September 8, 1942. In particular this invention relates to a combined centering and air ltering member for the bobbin and diaphragm assembly of an electrodynamic type of speaker having a moving voice coil or armature disposed in an annular gap in the magnetic circuit. As is well known, there is a tendency for any7 para magnetic particles suspended or moving in the nuid in which the unit operates to be drawn into this gap. Inasmuch as this gap is of relatively small area the presence of such particles in the gap disturbs the electrical and mechanical relationship of the movable parts and interferes with the effective operation of the speaker.

An advantage secured by the present improvement is the provision of a centering member for the inner end of a generally conical diaphragm assembly, which centering member is formed to function as a filter or screen excluding dust particles while allowing air to lter through.

Referring now to the drawing, Figure 1 shows a sectional elevation of a unit embodying this invention; Figure 2 is a section on line 2--2 of Figure 1.

The construction comprises a pot Ill provided in the center with a core Il both of magnetizable material such as soft iron or steel. Surrounding core I I and disposed inside pot I is a magnetizing coil l2. Pot I0 is adapted to be closed by a cover plate I3 having a plurality of apertures I 4 and whose inner edge portion I5 cooperates with portion I6 of the core to form pole pieces between which is an annular air gap I8. Cover plate I3 and pot I0 are of magnetizable material such as soft iron or steel so that upon energization of magnetizing coil I2 an intense magnetic field will be created within air gap I8.

Disposed within air gap I8 is a bobbin I9 of any suitable material such as ber upon which is disposed a Voice coil 20, having suitable leads for connection to a source of voice currents. Bobbin I9 is preferably provided with a series of apertures 2| disposed around it of such number and area as to permit movement of substantial quantities of air therethrough. The free end of bobbin I9 ls preferably closed by a generally conical dome shaped cap 22 which may be formed of light thin metal such as aluminum or copper or may be formed of thin fiber. The voice coil and bobbin are so proportioned as to move lengthwise within air gap I8 in the manner customary with such type of speakers.

Attached to bobbin I9 at the end thereof is a generally conical diaphragm 25 of any suitable material. This diaphragm may have the outer edge provided with annular corrugations 26 if desired. The diaphragm itself is formed of any suitable material such as stilfened paper, metal, phenolic impregnated cloth or any other material and has the outer end 21 thereof rigidly clamped by an annular flanged mounting portion 23 of a diaphragm housing 29. Housing 29 is provided with a mounting ange 3Il` suitably apertured to accommodate bolts 3l to maintain pot I0, front plate I3 and housing 29 rigidly in predetermined adjusted position. The entire speaker may be mounted by bolting annular ange mounting portion 28 to any suitable balile 32 in a manner well known in the art. Other methods of support are possible.

In accordance with the present invention, in order to center the small end of diaphragm 25 and bobbin I9 within air gap I8, a exible centering member 35 is provided. Centering member 35 may have the outer edge portion 36 rmly clamped in position and as shown here is firmly fastened to inner flanged portion 30 of housing 29. In order to securely fasten centering member 35, a rigid ring 31 suitably apertured to accommodate bolts 3l may be disposed outside of the centering member. In this Way, centering member 35 may be firmly and tightly clamped in position.

Centering member 35 has inner edge portion 38 securely fastened to the bobbin and diaphragm assembly I9 and 25. The fastening may be effected in any Way such as by cementing. The centering member may be physically attached either to the bobbin or to the diaphragm structure near the bobbin, the choice being one of convenience in manufacture. It is a unitary element consisting only of a single thickness sheet. Centering member 35 is porous and may be formed of fibrous material such as paper or cloth which has been impregnated with a stirfening agent, such as lacquer, varnish, phenolic compound or other substance which increases the strength and stiffness to a. desired degree. Thereafter it may be perforated if the material itself as fabricated is not suiiciently porous to act as a filter or screen. It is understood of course that the air flow impedance of the porous centering member may be relied upon to function as one of the determinants of the characteristics of the entire speaker.

Between centering member 35 and top plate I3 an annular chamber 40 is created whose volume normally is varied during voice coil travel. In order to reduce the effective or fractional volume variations to a minimum, apertures I4 in top plate I3 are provided so that the effective volume behind centering member 35 consists of chamber 40 and the additional chamber 4I in back of front plate I3. Obviously, the smaller the volume variations due to voice coil movement the less is the quantity of air passing through porous centering member 35, this being the sole air venting means. Hence the requisite porosity of member 35 Will be dependent upon volume variations.

In order to increase the axial compliance of member 35, corrugations as shown may be formed in the member, and to prevent any resonance effects such corrugations may be irregular and eccentric.

The entire speaker may be mounted in a suitable cabinet 3 of any suitable material. The back of the cabinet may either be open or closed with any suitable material and as shown here is closed with a sound absorbing material M. Another mounting for the speaker is shown in Figure l of the parent application previously referred to of which this is a division.

What is claimed is:

l. A member for holding the diaphragm assembly of a loud speaker in a centered position consisting of a single sheet of material having a substantially central opening to receive a diaphragm assembly and having distributed perforations therein of such size 4and number as to permit air to pass through them while preventingthe passage of dust particles through them.

2. A member for holding a diaphragm assembly as set forth in claim 1 in which the sheet is of thin inherently porous material.

3. .ii member for holding a diaphragm assembly as set Aforth in claim 1, in which the sheet is porous and is impregnated with a stiffening agent.

4. A member for holding a diaphragm assembly as set forth in claim 1 in which the sheet is inherently porous and is of a porous material impregnated with a stifiening agent.

5. A member for holding a diaphragm assembly as set forth in claim 1 in which the sheet is inherently porous and is of porous material impregnated with a phenolic resin compound.

6. A member for holding a diaphragm assembly as set forth in claim 1 in which the sheet is of porous material impregnated with a stiffening agent and thereafter perforated.

7. A combined air filtering and centering member for the bobbin and diaphragm assembly of a lloud speaker comprising a single sheet of flexible material having a substantially central opening to receive said assembly at the bobbin end thereof, said sheet having distributed per forations therein to permit air to pass therethrough while preventing the passage of dust particles, said sheet being impregnated with a stiiening agent whereby to provide an axially compliant centering support for the diaphragm.

HUGH S. KNOWLES.

REFERENCES CITED .following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,284,222 Buss Nov. 12, 1918 1,831,235 Barrow Nov. 10, 1931 1,886,816 Jensen Nov. 8, 1932 1,877,294 George Sept. 13, 1932 1,893,049 Baudette Jan. 3, 1933 1,997,051 Engholm Apr. 9, 1935 2,002,190 Round May 21, 1935 2,090,025 Brennan Aug. 17, 1937 2,261,110 Engholm Nov. 4, 1941 2,261,111 Engholm Nov. 4, 1941 FOREIGN PATENTS Number Country Date 351,204 Great Britain June 25, 1931 

